Sigurd Grindheim, «What the OT Prophets Did Not Know: The Mystery of the Church in Eph 3,2-13», Vol. 84 (2003) 531-553
The purpose of this essay is two-fold. First, it argues that the inclusion of the Gentiles is referred to as a previously unrevealed mystery because it is based upon the abrogation of the Mosaic law and entails a degree of nearness to the Lord that exceeds the expectations of the old covenant. Second, it addresses the question of authorship. Assuming Pauline authorship as a working hypothesis, it shows that the use of the concept of mystery in Eph 3 is intimately linked with Paul’s terminology and thought world attested in the undisputed letters. It is unwarranted, therefore, to find proof of a post-Pauline development in the use of the term "mystery" in Ephesians.
departure from the theology of Paul. In Paul, ecclesiology is determined by Christology, whereas in Ephesians it is the other way around: Christology is interpreted from the standpoint of ecclesiology63. That is why the inclusion of the Gentiles now can be understood as an adequate definition of the gospel.
It should be noted, however, that in Ephesians the gospel, or the mystery, is defined more broadly than simply as ecclesiology. The mystery is Christ and his reconciling work, encompassing the things in heaven and the things on earth (1,9-10)64. In a more narrow sense, corresponding to the earthly reconciliation, the mystery can refer to the unity of Jews and Gentiles in the church.
In the undisputed Pauline epistles the gospel can be described in a similar way65. The coming of Christ and the consequent abrogation of the Mosaic law result in a new status for the believers, where there is no distinction between Jews and Gentiles (Gal 3,25-29)66. In Rom 11,11-36, these ideas are expressed with a terminology that resembles that of Ephesians. The passage explains how the stumbling of Israel has resulted in the salvation of the Gentiles. This salvation is described as the reconciliation of the world (11,15; cf. Eph 2,16), the primary reference being the cross of Christ (cf. the parallel in Rom 5,10), but the resulting new relationship between Jews and Gentiles is also in view67.